The answer to the question posed in the title of this piece is actually extremely simple: Shea Weber. Or, to be more precise, it is that Shea Weber is a franchise defenceman who played frequently with Jones in the early going and has spent very little time with him since then.

In all but three of Jones’ first 17 games, his most frequent defence partner was Weber. In 35 of his last 36 contests, it has been somebody else. And while being paired with Weber means seeing the best opposition the other team has on offer, it also means playing alongside one of the greatest defencemen in the NHL today.

We can demonstrate how that has worked in Jones’ favour by looking at some newer statistics. Using timeonice.com, I have gone through every one of Jones’ games and identified three things in each game he has played:

Who Jones’ most frequent partner was

How many shifts started in the offensive/defensive zone

How many unblocked shots (commonly referred to as "Fenwick," after blogger Matt Fenwick who suggested this metric) for and against occurred with Jones on the ice

After identifying those numbers in each game, I tallied up the zone start and Fenwick numbers for Jones with each of his regular partners (in this example, players he spent five or more games with). The totals are on this chart:

Seth Jones by Defensive Partner

Partner

Games

Def. Z

Off. Z

Fenwick+

Fenwick-

Adj. Fenwick

Shea Weber

15

112

88

188

182

52.2%

Mattias Ekholm

14

68

56

160

159

50.9%

Ryan Ellis

8

14

36

73

66

50.0%

Kevin Klein

7

28

35

61

82

40.6%

Victor Bartley

5

23

17

35

56

37.8%

TimeonIce.com

What is that “Adj. Fenwick” column at the end? What we have found is that when a player starts more frequently in the offensive zone, his team gets more shots (duh) and vice versa in the defensive zone (duh, again). So while a 50/50 split is the break-even mark for a guy who has an equal number of offensive and defensive zone shifts, most players see more of one than the other.

Adjusted Fenwick is a way of compensating for that. Here we use Eric Tulsky’s method for negating those extra shifts in the offensive or defensive zones so that what we are looking at is Jones’ expected Fenwick rating with each partner if all of those tandems had equal numbers of offensive and defensive zone starts.

Brace Hemmelgarn-USA TODAY Sport

It’s a long explanation, but the results are remarkably straightforward. When paired with Weber, Jones has been an exceptional NHL defenceman. When paired with Mattias Ekholm or Ryan Ellis, he’s been pretty decent. Finally, when paired with Kevin Klein or Victor Bartley, he’s been awful.

Defensive partners go a long way toward explaining Jones’ season. He was very good early, when he played alongside Weber. Then came a long middle stretch where he bounced around from partner to partner, during which Jones struggled badly. He’s rebounded somewhat over the last while, playing on a stable pairing with Mattias Ekholm.

The upshot of all this is that for all his talent, Jones is not a difference-maker at the NHL level right now. That should not come as a surprise; very, very few 19-year-olds can step into the major leagues and be bona-fide first pairing rearguards.

Jones, with a lot of help from Weber, impersonated one for longer than most. In its later stages together, that tandem started struggling to drive play, resulting in its breakup, and when Jones was placed with other partners, he revealed himself as the struggling defenceman he was.

Jones has been better of late as his game evolves, and doubtless that trend will continue until he reaches his full potential.